Thank you for the open sourcing of that lib. It looks great.
> There's no point open-sourcing the crappy old parts of our architecture which we wouldn't advise new projects to use
Well, there is an educational point to be made about this... :)
I think too many people in open source focus on "if it's open source, it must be great, look great" etc. I for one put every crappy project I start and never complete on Github along with the good ones I'm proud of. Because I like my "learning process" being out in the open as well. I don't publish my hello-worlds of course but I don't specifically hide stuff people "I believe should not use". Warnings in the readme are as far as it goes.
My company systematically opens its entire process to the public. All the code is on Github, all the issues are there too. Our internal discussion/design process is on IRC, Google Docs and the Github wiki and they are all public and archived. Only client work under NDA remains private.
Google has a similar-ish model for some open source projects it released. I wish more companies would adopt a model like this. Well, of course, open sourcing important frameworks and useful stuff remains a higher priority... but I don't believe there is any harm in it, and it actually holds the employees to a subconscious "higher standard".
I'd love to talk more about it but I think I'm getting off-topic here. Once again, congratulations on the release!